U.S. Supreme Court Justice Antonin Scalia, the leading conservative voice on the high court, has died at the age of 79, a government source and a family friend told CNN on Saturday.

His death set off an immediate debate about whether President Barack Obama should fill the seat in an election year. Obama said Saturday night that he plans to nominate a replacement, but Senate Majority Leader Mitch McConnell said the nomination should wait until the next president comes into office while top Democrat Harry Reid called for the seat to be filled "right away."

Scalia died in his sleep during a visit to Texas. A government official said Scalia went to bed Friday night and told friends he wasn't feeling well. He didn't get up for breakfast on Saturday morning, and the group he was with for a hunting trip left without him.